A computer network is a collection of interconnected computing devices that exchange data and share resources. In a packet-based network, such as the Internet, the computing devices communicate data by dividing the data into small blocks called packets. The packets are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission. Computer networks may divide data into other types of data units, such as cells or frames.
The computing devices may be interconnected by one or more links. The term “link” is often used to refer to the connection between two devices on a network and may include a physical medium, such as a copper wire, a coaxial cable, or any of a host of different fiber optic lines, or a wireless connection. One or more devices of the network and/or one or more links of the network may fail due to any of a number of reasons. When a device or link of the network fails, the result is a loss of service to particular customers, which is generally undesirable. An administrator of the network would therefore like to limit the amount of time of the failure.
Operations, Administration and Maintenance (OAM) generally refers to processes, activities, tools, standards and other techniques that involve operating, administering and maintaining, e.g., troubleshooting, a computer network. One such OAM techniques, such as Connectivity Fault Management (CFM) as described in the IEEE 802.1ag standard, may include a number of proactive and diagnostic fault localization procedures. For example, a network device operating in accordance with CFM may proactively transmit connectivity check (CC) messages at a predetermined rate to other devices within the same maintenance association, i.e., a logical grouping of devices within the network configured to verify the integrity of a single service instance. A service instance may, for example, represent a portion, e.g., network devices, of a provider network that a given customer can access to query a status of services delivered for that customer. The CC messages provide connectivity verification to the other network devices within the maintenance association. The other network devices in the maintenance association may create and maintain a connectivity database of network devices from which periodic CC messages are expected to be received. The network devices may, after establishing connectivity with the other network devices, monitor receipt of CC messages. If a CC message is not received from one of the network devices identified in the connectivity database within a configured time, the network device may identify a failure of the device from which the CC message was expected to be received. This failure is commonly referred to as a “connectivity failure.”
A network device operating in accordance with CFM may also include a number of reactive procedures for identifying fault locations, such as loopback and link trace messages. A loopback message is transmitted from a first network device to a second network device. If the second network device is in front of the fault, the second network device responds with a loopback reply. If the second network device is behind the fault, the second network device may not receive the loopback message and may therefore fail to responds with a loopback reply. The precise location of the fault within the maintenance association may be identified based on whether the first device receives the loopback reply. Other OAM standards, such as those defined in ITU-T Y.1731, IEEE 802.1ab, IEEE 802.1ah and ITU G.8031, may include similar proactive and diagnostic procedures.